Gas injectivity profile logging



Nov. 21, i961l E. F. EGAN ET AL GAS INJECTIVITY PROFILE I .OGGING Filed Nov. l2, 1957 United States Patent G 3,010,023 GAS INJECTIVITY PROFILE LOGGING Edmond F. Egan, Richard H. Widmyer, and Alexander S. McKay, Houston, Tex., assignors to Texaco Inc., a corporationV of Delaware Filed Nov. 12, 1957, Ser. No. 695,903 14 Claims. (Cl. Z50- 106) This invention relates to a method and apparatus for studying subsurface earth formations and more particularly to a method and apparatus for measuring the permeability of earth formations traversed by a well or borehole.

Knowledge of the permeability of subsurface formations in petroleum operations is of considerable importance. In secondary recovery operations for the production of oil from subsurface formations a fluid, for example water, oil or gas, is pumped into an injection well located at a point remote from an oil production Well and directed into a given formation or vertical interval in the injection well to urge oil which may be contained therein toward the production well. In order to determine whether the uid pumped into the injection well is being efficiently injected into the given formation the amount of fluid passing into various vertical increments of the wall of the injection well must be known. A log which indicates the vertical increments of the injection well into which uid is entering and the amount of fluid flowing into each increment is sometimes referred to as an injectivity profile or permeability log of the Well.

A method of obtaining an injectivity profile or permeability log of a well or a particular formation traversed by a borehole has been described in U.S. Patent 2,700,734 granted to Edmond F. Egan and GerhardHerzog on January 25, 1955. In the patented method two streams of tluid are pumped into a Well, one stream passing through a string of tubing extending downwardly to a point below the formation of interest and the other stream passing downwardly through the annular space between the tubing and the casing or the wall of the well. The streams are pumped simultaneously and each stream is carefully metered at the surface. The fluid pumped down throughthe tubing will, after lling the exposed portion of the well below the tubing, iloW upwardly around the .tubing until it meets `the uid pumped downwardly through Vthe annular space, thus forming an interface between the two streams or bodies of fluid. In order to llocate the interface between the,l two streams a small amount of tracer material, suchas a radioactive substance, is added to one of the Ystreams before it enters ,the well so that all of the uid in this stream will be radioactive while the other stream will be non-radioactive.

The depth in the well at which the interface lies may be ing into a vertical incrementof the formation of interest j the rates of injection or pumping of `each of thetwo Patented Nov. 21, 1961 ing appropriate changes in the ratio 0f the amount of radioactive iluid to the amount of non-radioactive fluid pumped into the well the interface can be moved in a number of steps through the well past the formation of interest to provide an accurate log of the permeability of the formation, the length of each of the vertical increments between successive interfaces depending upon the amount of change of the rates of the two streams and upon the permeability of the increment. After each adjustment or change in the rates of the two streams the radiation detectoris passed through the well and a record is made of the rates of the two streams and the depth of the interface. Accordingly it can be seen that in this manner an injectivity profile is made of a formation which clearly shows the permeability of the various vertical increments of the formation.

In accordance with this invention there is provided an improved method and apparatus for producing a gas injectivity profile log of a Well. The method comprises supplying a gas stream under pressure to a conduit leading into the well and pumping an organic liquid solution of a radioactive organic compound through a flow regulating orifice into the gas stream in the conduit in a minor proportion by weight based on the weight of the gas, the organic liquid solution containing the radioactive organic compound being a liquid when in a sealed or enclosed container but both the organic liquid and the radioactive compound vaporizing rapidly when introduced into the owing gas stream.

In order that the invention may be more clearly understood and readily carried into effect it will now be described more fully with reference to the accompanying drawing in which:

FIG. l is a vertical sectional elevation through a well illustrating apparatus for producing a gas injectivity profile log and FIG. 2 is a cross section of a type of flow regulating and atomizing needle valve which may be used in the apparatus illustrated in FIG. l. 1

Referring to the drawing in more detail and particularly to FIG. l," a well or borehole 10 is shown traversing jseveral subsurface formations including the subsurface vformation 12 for which it is desired to make a gas injection profile. The upper portion of the well is shown as being provided with a `casing 14v having a closed casing head 16. A string of tubing 18 passes through the casing head 16 and downwardly through the well 10 to a point below the formation 12. Shown as suspended within the tubing 18 is a radioactivity logging instrument 20 containing a detector of gamma rays, the output of which is conducted upwardly through a conductor cable 22. The conductor cable 22 passes through the tubing 18 and a suitable well head'lubricator shown in part at 24 and over a pulley 26 and a cable measuring drum or reel 2S which serves to indicate the amount of cable payed out and therefore the location of instrument 20 in the well 10. The upper end of the cable 22 is connected'to a suitable indicating device 30, for example,

a meter, oscilloscope 0r a recorder of the permanent lthrougha main flow valve 36, for example a needle or gas regulator valve. The gas from the main flow valve 36 is then split into two streams, the first stream passing through ,a first proportioning or regulating needle valve 38, a firstorice meter 4Z, a 2-way valve 44, and a first shut-off valve I46 into" the tubing 18 through a T 48, and the second stream passing through a second propor- Vtioning or regulating needle valve 52, a second orifice -meter 54, the 2-Way rvalve 44, and a second shut-off valve 56 into the annular space between the casing 14 and the tubing 18. A pump 58 connected to a tank or reservoir 60, preferably of a closed type, which contains a liquid tracer material, pumps the liquid through a suitable flo-W indicator Si), a shut-off valve 51 and a valve 62 which preferably may be adapted to atomize the liquid into the second gas stream before the gas enters the Well. Alternatively, the pump 58 may be connected through the flow indicator 50 and a shut-off valve 53` to a second valve 64 when it is desired to introduce the liquid from tank `60 into the first gas stream. Since the liquid tracer material may not immediately completely vaporize in the stream at the outlet of the valve 62 the conduit or line lconveying the gas stream between each of the first and second valves 62 and 64 and the well head Should slope downwardly toward the well head so that any unvolatilized tracer solution will not ow upstream Where it may be trapped, as for example, in a valve bottom. The sloping section of the line leading to the well head should be free of liquid traps.

A cross section of the type of valve which may be used for valve 62 or 64 is illustrated in more detail in FIG. 2. This valve, which is a needle valve, has an inlet 66 and a relatively small outlet 68, for example, 1A diameter, into which the needle 70 may be inserted by operating knob 72. Liquid is pumped through the inlet of this valve and remains in its liquid form until it passes through the outlet 68 where it is atomized and injected into the gas stream at a rate suicient to produce a clearly identiiiable interface 74 between the two gas streams in the Well 10.

When making a gas injection survey wherein the tracer material is a radioactive substance, a natural gamma ray log of the borehole may lbe obtained before theradioactive substance is introduced into the well. This log serves as a base or reference line for comparison with future logs made during the survey. A base log is not necessary when the contrast between radioactive and non radioactive gas is large or when the tubing stream 'is being tagged.

After this reference log is .obtained the radioactive substance is injected into the gas stream which is being conducted into the annular space between the tubing 18 and the casing 14 until an interface is established at the top of the formation of interest. This interface is ilocated by 4producing' a radiation log of the hole with the radioactivity detector 20' and comparing this log with the original base or reference log, the lowest point of radioactivity increase indicates the radioactive-non-radioactive interface and thus locates the depth of the interface. Depending on the concentration of radioactive `material in the tagged or marked lgas in the annulus the point of increase in radioactivity over the natural background may stand out sharply enough so that a comparison vwith the reference log may not be necessary. Ordinarily if there is sudcient radioactivity in the tagged gas to give a reading from the detector of at least about three times the background value the interface will be v'clearly distinguishable without making a comparison with the-reference log.

An injectivity profile is built up by a systematic incremental adjustment of the rates of flow of the gasstreams, combined with a determination of the location of the interface between the radioactive andV non-radioactive streams for each adjustment of the gas -streams by the radioactivity detector 20. To move the interface Vinthe downward direction, the flow of the nonLradioactive gas which is-being supplied to the tubing is reduced by about l0 percent and simultaneously the flow of the radioactive gas in the annulus is increased by the amount which the radioactive gas was decreased, thus to maintain a constant total ilow into the well. Injection is maintained at these new rates until a stable condition is attained. The logging instrument 20 is then moved through the tubing 1S to locate the new position ofthe interface. As

the ratio of radioactive gas in the annulus to non-radioactive gas in the tubing is increased, more of the permeable zone will be exposed to the injection of radioactive gas. Injection pressures encountered can range from a low of 20-25 p.s.i.'a. 'to as high or higher than 5000 p.s.i.a. and the total volumes can range from 50 to 50,00() standard M c.f .d.

It is not necessary that the incremental 'change in flow rates follow any set arithmetical pattern. The incremental changes should be such that the results can be plotted in terms of percent input of the tagged stream against the borehole depth, the plotted points being spaced close enough together to present an accurate indication of the injectivity profile.

The selection of a suitable radioactive tracer material for tagging one of the two streams of -gas is made on the basis lof several factors, such as, (l) It should contain an economical gamma decay type radioactive isotope having a reasonably short half life; (2) It should be a liquid in order to facilitate handling and to permit the use Yof the same injection equipment which is used for liquid tracers in liquid injection surveys; (3) It should have lfairly high vapor pressures at injection temperatures to facilitate vaporization in the gas stream but the vapor pressure should not be so high 'as yto produce handling hazards; and (4) It should be soluble in a suitable `diluent having approximately the same physical properties.

In accordance with an important feature of this Ainvention 'it has been found' that certain compounds of iodine 131, rparticularly ethyl iodide and methyl iodide, meet these isotope requirements. Ethyl alcohol has been found to be a suitable solvent and carrier liquid for ethyl iodide, and this combination is particularly suitable for tagging gas under nor-mal conditions `of temperature in temperate or warmer climates. Under certain 'conditions, for example, when tagging gas under low atmospheric temperature conditions, or When the gas is -cold as results from passage 'through an expansion valve, it is desirable to use the combination of methyl iodide and methyl alcohol instead ofthe ethyl iodide-ethyl alcohol combination in accordance with the teachings of this in- `vention.

Radioactive ethyl iodide is available on the market as 'a concentrated solution yin ethyl alcohol which can be transported in a sealed container. yThe tot'al volume of this concentrated tracer solution vnecessary to obtain a complete permeability-log of vajgiven formation may vary Strom, for example, Aabout 1A -to v3 'ounces providing 4from 5 to 50 lmillicuries 'of ethyl iodine. This total volume kof concentrated tracer solution is mixed Vin the tank 60 l*with a'much larger volume of ethyl alcohol, for example, about 2 to 4 gallons, before it is injected into one fof the Ytwo streams which vare introduced into the well.

The Irate 'at which the 'tracer solution is injected into vfone of thet'wo y-gas streams may be controlled Vby utilizing 'a calibrated AVernier mechanismcontrolling :the length Jof 'the piston 'stroke of the positive displacement pump 5'8. The flow indicatoirfSt) may beused to provide a vvisual indication of tracer solution'tiow into the 'gas stream. When the gas stream which is directed -into (the annulus is to be taggedwith the radioactive 'tracer "material, shut-oli:` valve 53 is in its lclosed lpositio'n and shut-off valveSl is in its open position to -thuspermit the tracer material to pass through the tracermaterial 'atomiziing "needle valve 62. When lit is desired to tag the stream entering vthe wellthrough the tubing 18 shut-olf valve '51 is in its dlosed position and yshut-off valve 53` is in its open position to permit the tracer material to pass through the tracermaterial atomizing needle valve "64. During the logging operation the Yrate of tracer solutioninjection 'is varied in a direct ratio with any changes in 'rateof the gas stream into which it is being fed so 'that the concentration of `tracer, material 'in the tagged :stream iis maintained constant.

Although ethyl iodide and methyl iodide compounds have been identified as suitable tracer materials it should be understood that any other radioactive tagging chemical may also be employed 'which is sufficiently volatile to vaporize readily in the gas stream to provide a uniform concentration of the desired amount of tracer, which has a very low solubility in fresh and salt water and which has low or negligible reaction with water.

In measuring the lamount of gas owing in the streams the accuracy of the meter readings is dependent upon the size of the orifice with respect to the gas flow rate and pressure. Generally, the variation of flow rate in gas injectivity logging covers too great a range to permit accurate readings with the use of Aa single orifice. To eliminate the need for changing orifice plates the apparatus of this. invention, as illustrated in FIG. l, includes switching means for readily interchanging the ori-tice meters 42 and 54 so that one meter measures rates only from to 50 percent of the total flow of gas into the well and the other measures rates only from 50 to 100 percent. Thus, when the ow to the annulus constitutes 0 to 50 percent of the total gas, the low rate meter is connected to measure the amount of gas ilowing to the annulus and the high rate meter is connected to measure the gas flowing to the tubing 18. However, when the flow rates are altered so that the gas flow to the annulus reaches 50 percent or more of the total gas, the meters 42 and 54 are switched merely by the operation of the 2-way valve 44. The high rate meter will then measure the flow of gas to the annulus and the low rate meter will measure the ow to the tubing 18. In this switching method the proportioning valve 38 at all times controls the amount of gas flowing through orifice meter 42 and the second proportioning valve 52 at al1 times controls the flow of gas measured by second orifice meter 54. The stream measured by the low rate meter is fed into the annulus when the stream being fed thereinto is 0 to 50 percent of the total gas and thereafter it is directed by Zaway fvalve 44 into the tubing 18. It should be understood that the functions of the valves 38 and 52 may be performed by utilizing a suitable single proportioning valve at the common point of origin of the rst and second streams, i.e., at the junction point between valves 36, 38 and 52. v It should also be understood that the switching function of the Z-way valve 44 maybe performed by using other apparatus. When a two-way valve is not interposed in the conduit between the meters 42 and 54 andthe shut-off valves 46-and 56, conduits each having a shut-off valve therein may be connected from the upstream sides of each one of to the downstream sides of each of the other of the shut-olf valves 46 and 56.

Although in the description of Athe method which has Ybeen given it has been stated that the interface 74 is moved downwardly in increments along the wall ofthe formation 12 it is to be understood that the permeability log of the formation can be made upwardly yas well as downwardly. Thus the interface 74 can be positioned rst at or just below the lower boundary of the formation 12 and then the pumpingrates of the two gases are changed by decreasing the rate of the stream pumped into the annulus and increasing the rate of the stream pumped into thetubing 18 by the same amount so that the interface 74 will move upwardly to a new positionf This new position of the interface may, then be foundashas beenkv described by moving the Vinstrument 20 through the tubing-18. This operation may be repeated until the interface 'has-'65:

c@der normal atmospheric temperatures and pressures, but *both the organic liquid and the'radioactive compound reached a point at or just above the upper boundary of the formation 12. The resulting log obtained in this manner will be the same as a log obtained by moving the .interface downwardly. n

Arlthough the radioactive gas lhas been described as' lbeing pumped down through the annular space between the. tubing and ,the non-radioactive gas through the annulus without affecting the process.

The apparatus illustrated in FIG. l shows that the two gas streams, that is, the radioactive and non-radioactive gas streams, are being pumped by one pump 34. .It is to be understood that two pumps, one to pump the radio- Aactive gas stream and the other to pump the non-radioactive gas stream, may be used.

Obviously, many modifications and variations of the invention as hereinabove set forth may be made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims. 1

We claim:

1. In injectivity profile logging of a well, the method which comprises introducing a gas stream into the well and injecting an organic liquid solution of a radioactive organic compound in atomized form into the gas stream in a minor proportion by weight based on the weight of the gas, said organic liquid and said radioactive compound vaporiziug rapidly in the flowing gas stream.

2. Ihe method according to claim 1 wherein the radioactive compound is Rlm, where R is a lower alkyl.

3. Ininjectivity profile logging of a well, wherein a stream of gas is introduced into a well, the gas containing a radioactive material, and a radiation detector is moved through the well to determine ow characteristics of the gas stream, the method which comprises supplying the gas stream under pressure through a llow regulating valve to a conduit leading into the Well, and pumping an organic liquid solution of a radioactive organic compound through a ow regulating oriiice into the gas stream in said conduit in atomized form on the downstream side of said rst mentioned ow regulating valve in a minor proportion by weight based on the weight ofthe gas, said organic liquid and the said radioactive compound vaporizing rapidly when in the flowing gas stream.

v4. The method according to claim 3 wherein the said radioactive organic compound is RIm, wherev R is a lower alkyl. `5. The method accordingto claim 4 wherein the organic liquid is selectedV fromthe group consisting of methyland ethyl alcohol, and the R of the said radioactive, organic compound RI131 is selected from the group consisting'V of methyl and ethyl.

I6r, The method according to claim 3 wherein both the rsaid organicliquid and the said radioactive organic compound are normally liquid at atmospheric temperatures and pressures and have boiling points under standard vconditions above 50 C. and below 85 C.

Y 7. The method according to claim 3 wherein the said organicliquid is ethyl alcohol, and the said radioactive v 8. The: method of making'a log 'in a borehole which comprisesr pumping a gasinto` said borehole in a downward direction, simultaneously pumping another gas through said borehole in an upward direction so as to establish an interface Abetween said gases, simultaneously `vpumping' into one of said gases'and atomizing an or- Vganic liquid solution ofa radioactive organic compound vin a` minor proporti-onby weightrbased on the Weight of'said one gas, said organic liquid solution containing the said radioactive compound being a liquidl unvapprizing rapidly vwhen atomized into said one gas, de-

terminingithe depth in thehole "of said interface, varying the ratio of the rates ofl theitwo gases lbeing pumped into the". hole While maintaining constant the sum 7'of the rates of the two liuids so as to cause said interface to moveralongthe wall of said borehole to another depth, again determining the 4'depth of'the interface, and repeating these operations while noting the distance 'moved by the interface 'for each change in ratio of the rates of the two lgases being pumped into the borehole.

9. The' method of `nia'kir'rg 'a permeability log of a subsurface formation traversed by a Aborehole containing a tubing extending down below said formation which comprises injecting a rst stream of gas into the `annular space between the tubing and the walls of the hole, simultaneously injection a second stream of gas into said borehole below said formation 'through said tubing, lintroducing an organic liquid solution of the `radioactive compound in atomiz'ed Vforr'n into oneA ofsaid streams in a minor proportion by Weight based o'n the weight of the gas in said one stream, said organic liquid and radioactive compound voporizing rapidly when in said one gas stream, whereby an interface between the gases of said first and second streams is established, determining the ydepth in the hole of said interface by measuring the radioactivity 4of the lgas content throughout that portion of the hole being examined, varying the ratio of the two gases being pumped in'to the hole while `maintaining constant the sum of the two gases so Aas to cause the interface tomove along the walls of said formations to another depth, determining again the depth .of the interface by making another radioactivity measurement of the contents of the hole and repeating .these operations while noting the ratios of the two gases of the streams for each measured depth of the interface in the borehole.

10. Apparatus for making a permeability log of a subsurface formation traversed by a borehole containing a tubing extending down below said formation in said borehole, comprising means for supplying Afirst and second gas streams to said borehole, one of said gas streams being injected Ainto said tubing and the other of 'said streams being injected into the annular space :between said tubing .and the wall of the borehole, gas measuring -means including first and second orifice meters each having-dilferent ranges Vand adapted to measure 'the amount of gas in a diiierent one of said streams and switching means for interchanging said meters with respect .to said -first and .second gas streams, means 'for 'injecting .a liquid traCermaterial I'into one ofsaid streams in atomized form, .and .detecting means disposed .in said borehole lfor deter; mining the depth in the hole ofthe interface between the ,gases .of .the .first .fandsecond streams.

.11. Apparatus Yfor making a l`permeability log 'of a vsubsurface formation vtraversed b y a borehole containing `a `tubing .extending down Ibelowjsaid formation comprising a gas supply system including pumping means 'and .main control means, means 'for conveyingjirst 'and sec- Yond .gas .streams from said .gas supply system finto said borehole, said conveying Ameans including first andnsecfond .proportioning means, each of said proportioning means being adapted to regulate the flow cfa .different VAone ,of fsaid ,gas streams, one l of said .gas vstreams being* conveyed :into the borehole 'through said tubing and the `other ofksaid streams being conveyed into the annular space rbetween .said vtubing andk the wall of .the borehole,

gas measuring ,means coupled 'to said conveying means and including first and second orifice meters each 'adapted means for selectively .introducing `into one .o`f said iirst and-second streams ,a liquid tracer material `in atomized form Iin a minor proportion by weight vbased on the weight ofthe .gas .of said'o'nestre'am, said introducing meansincluding a reservoir for storing an organiclliguid detecting 'the interface between said first and second streams. l

- 12. Apparatus for making a permeability log of a subsurface formation traversed by a borehole containing a tubing extending down from said vformation comprising a gas supply system including pumping means and a main control `needle valve, means for conveying first and second gas streams from said gas supply system into said borehole, said conveying means including first and second proportioning needle valves, each of said proportioning needle valves being adapted to regulate the iiow of a different one of said gas streams, one of said gas streams being conveyed into the borehole through 4said tubing and vthe other of said streams 'being conveyed `into the annular space between said tubing and the wall of the borehole, gas measuring means vincluding -a low rate orifice l meter and a high rate orifice meter each adapted to measure the amount of gas viiowing in a different one of said streams and a 2-way valve for interchanging said meters, means `including ya needle valve coupled to said conveying Vmeans for selectively atomizing directly -into one of said first land second gas'streams Ja liquid tracer material lin a minor proportion byV weight based on `the weight of the gas of said one stream, and detecting means disposed in Asaid borehole for 'detecting the interface between said first and `second streams.

i3. Apparatus for `making a permeability log'of a subsurface formation traversed by a "borehole Vcontaining a .tubing extending down Vbelow said `formation in said borehole comprising gas lsupply means f or conducting rst and second gas streams, `said means 'including a proportio'ning means for controlling and an orifice meter formeasuring the rate Vof iiow of gas in each of the streams, .one of said meters 'being a low rate Ameter, and `the other being la high rate meter, 'first and Isecond means for conveying said y.gas streams into said 'tubing and into the annular space between said tubing yand the wal-l -of the 'borehole respectively, switching means interposed b etween Vsaid conducting means 'and said first vand -second conveying Vmeans .for selectively 4directing 'said 'rst'and ,Secondgas streams into said first and second conveying means, means for selectively atomizing aliquid tracer material intoone of said first and second gas streams and .detecting means 'for determining the depth inthe borehole of the 'interface between the gases lof said "iirst 'and secondstreams.v

V.14. Apparatus for making a'permeability log o'f a rsubsurface .formation traversed by a borehole containing a tubing extending ldown below said vformation in said .borehole .comprising .first and second means for conducting .first .and .second Ygas streams respectively, each of .said .conducting ,means `including `a proportionng device ,for controlling ,and .an orifice meter V'for measuring the rate of .flow of gas, irstand secondmeans for conveying :said ,gas streams :intosaid tubing and "into 'the .annular vspace rbetween :said tubing .and the `wall of ,thefborhole respectively, means `for selectively `interconnering said conducting means `and .saidconveying meanslfol the si- -nnultaneous.flow of lsaid gas streams through both ofsaid ilastementionedv means, means for selectively ,pumping .a '.-radioactiv-eA vapor -iuto rone .of .said .first Yand Ysecond ,gas

rstreams .and radioactivity detecting .means for ,determin- ,ing the depth :in fthe .borehole of .the 'interface between the gases of` the `rfirst -andsecond streams. Y

References .Cited intheifile of .th'ispatent *eUni-ren s'rArns PATENTS solution .of -aV radioactive organic compound," a needle v70./2,'453f456f` '19218 `valve :disposed `to discharge-s .a'vapor directly ,into `onejof .2,518,307 195,0 the gas streams .and .means Aforpumping the'fliquid solu- .2,634,242 `1953 tion vfrom said :reservoir to .said needle valve, and radiog V2,700,734 i 1955 :activity detecting means .disposed fin said "borehole 'for ,Hull Mar. 1'1, 1958 

